Rock mechanics and engineering. Vol. 5. Surface and ungerground projects

0488267 - GFÚ 2018 RIV US eng M - Monography Chapter
Šílený, Jan - Milev, A.
Mechanism of mining-associated seismic events recorded at Driefontein - Sibanye gold mine in South Africa.
Rock mechanics and engineering. Vol. 5. Surface and ungerground projects. Boca Raton: CRC Press, 2017 - (Feng, X.), s. 349-376. ISBN 978-1-138-02763-3
R&D Projects: GA ČR GAP210/12/2235
Institutional support: RVO:67985530
Keywords : alternative source models * resolution - confidence zones * shear-tensile crack dominance
OECD category: Volcanology

Mode of fracturing of the rock mass is the key point in rock mechanics
applied both to natural earthquakes foci and to sources of induced or triggered
seismic events. The parameter providing the answer is the source mechanism. The
moment tensor, currently used as a universal tool for descriptions of the mechanism,
involves general balanced dipole sources. However, in case of small-scale seismic
events, the moment tensor need not be always reliably determined. In an effort to fit
the data, there may be notable non-shear components caused by the low quality of
input data. It means that while the orientation of the fracture is usually estimated
well, the mode of fracturing itself may be dubious. Constraining the source model to
directly determine a simpler one is convenient for describing the physical phenomena
expected for a particular focus. An opening of new fractures can be described, to a
first approximation, by a tensile crack, optionally combined with a shear slip. Such an
alternativemodel is called a shear-tensile crack (STC) sourcemodel. The combination
is practical, and can be used to both identify events that reflect purely mode-I (tensile)
failure and to determine the dilation angle of the fracture undergoing shear. The
advantage of the STC is even enhanced in application to mining tremor foci, as
implosion (i.e., tensile process with a negative sign) can be reasonably expected
there as the consequence of collapsing mined-out cavities. From the technical point
of view, the STC inversion is more robust than theMT one thanks to smaller number
of the model parameters (5 vs. 6), which is crucial in cases of a poor monitoring
configuration.
Permanent Link: http://hdl.handle.net/11104/0282866